The invention relates to electric household appliances in general, and more particularly to improvements in electric irons, especially steam irons.
The sole plate of a portable electric iron is normally heated by one or more electric resistance heaters which are installed in the interior of the housing. Each resistance heater includes one or more wire-like resistors which can be connected in circuit with a source of electrical energy whereby the resistors emit heat which is directed into the sole plate. The resistance heater or heaters can be installed in the sole plate. Such heating systems exhibit a number of serious drawbacks. Thus, the initial and assembly cost of electric resistance heaters is rather high, especially since they must be mounted on carriers of electrically insulating material. Moreover, it takes a relatively long interval of time to heat an electric resistance heater until it begins to emit heat at the desired rate, and it takes a relatively long interval of time to ensure that an electric resistance heater is adequately cooled upon completion of an ironing operation. Thus, large quantities of heat energy are lost during heating and cooling of the sole plate; this evidently entails huge losses in electrical energy.
It is further known to equip portable electric irons with any one of a wide variety of sole plates. For example, a conventional sole plate can be made of a single piece of metallic material, especially aluminum or steel. An advantage of aluminum is that its heat conductivity is quite satisfactory and that its specific weight is relatively low; however, the ability of an aluminum sole plate to resist scratching, scoring and similar damage is unsatisfactory. A sole plate which is made of steel is more resistant to wear; however, its weight is rather high and its thermal conductivity is not satisfactory.
It was already proposed to make a sole plate of two pieces consisting of different materials. For example, a main body portion or core which is electrically heatable and is made of aluminum carries a thin-walled base plate of steel which comes in actual contact with the article to be ironed. This not only increases the cost of the sole plate and of the entire iron but also brings about other drawbacks. For example, if the iron is a steam iron so that the sole plate must have openings for discharge of steam, the relatively thin base plate tends to undergo permanent deformation in the region of such openings. This imparts to the article-contacting surface of the sole plate an undulate or other undesirable shape which affects the quality of the ironing operation.